White light emitting device and method of making same

ABSTRACT

A white-light emitting device comprising a first PRS-LED and a second PRS-LED. The first PRS-LED has a primary light source to emit blue light and a secondary light source to emit red light responsive to the blue light; and the second PRS-LED has a primary light source to emit green light and a secondary light source for emitting red light responsive to the green light. Each of the primary light sources is made from an InGaN layer disposed between a p-type GaN layer and an n-type GaN layer. The secondary light sources are made from AlGaInP. The primary light source and the secondary light source can be disposed on opposite sides of a sapphire substrate. Alternatively, the second light source is disposed on the n-type GaN layer of the primary light source. The second light sources may comprise micro-rods of AlGaInP of same or different compositions.

FIELD OF THE INVENTION

The present invention pertains to the field of semiconductoropto-electronic devices. More specifically, the present inventionpertains to white light emitting diodes.

BACKGROUND OF THE INVENTION

Light emitting diodes (LEDs) are special types of semiconductor diodesfirst developed in the 1960s. A simplest LED consists of a p-typesemiconductor and an n-type semiconductor forming a p-n junction. Whenan electric current passes through the junction, it createscharge-carriers (electrons and holes). In the process, an electroncombines with a hole and releases energy in the form of a photon. Mostof today's high efficiency LEDs have one or more layers of lightemitting materials sandwiched between the p- and n-type regions toimprove the light emitting efficiency. The layer structure is also usedto obtain desired emission wavelengths. The basic structure of an LEDdevice consists of a small piece of such layered material, called a die,placed on a frame or a baseboard for electrical contacts and mechanicalsupport. The die is also encapsulated for protection.

With an LED, the wavelength of the emitted light is determined by thebandgap energy of the light emitting material. One type of materialsuitable for LEDs is the compound semiconductors having bandgap energiescorresponding to near infrared (IR), visible or near ultraviolet (UV)light. AlGaInP (Aluminum Gallium Indium Phosphide) is one of the LEDmaterials that exhibit high quantum efficiency (hence high brightness)and versatile colors. The bandgap of (Al_(x)Ga_(1-x))_(1-y)In_(y)P alloysystem varies, depending on the x and y in the composition. The color ofAlGaInP LEDs ranges from green to red.

AlGaInP LEDs must be fabricated on a lattice-matching gallium arsenide(GaAs) substrate using an epitaxial growth process, such as themetalorganic chemical vapor deposition (MOCVD).

In the 1990's violet, blue and green LEDs based on gallium nitride (GaN)materials were developed. GaN is a direct bandgap semiconductor withbandgap energy of ˜3.4 eV. The electron-hole recombination in GaN leadsto emission of photons at a wavelength of 360 nm, which is in the UVrange. The visible wavelength LEDs (green, blue and violet) are achievedby using In_(z)Ga_(1-z)N as the light emitting layer, sandwiched betweena p-type GaN layer and an n-type GaN layer. The wavelength λ of thelight emitted by the In_(z)Ga_(1-z)N LED system varies depending on thez value. For example, for pure blue color, λ=470 nm, z=0.2. The GaN LEDsmust be fabricated on a lattice-matching substrate such as sapphire orsilicon carbide (SiC), again using epitaxial growth processes such asMOCVD.

Great efforts have been made to produce white LEDs as a replacement forconventional lighting sources. Currently, white color LEDs can beaccomplished in various ways:

(1) Putting discrete red, green and blue LEDs in a “lamp” and usevarious optical components to mix light in red, green and blue colorsemitted by those discrete LEDs. However, because of the differentoperating voltages for LEDs of different colors, multiple controlcircuits are required. Furthermore, the lifetime of the LEDs isdifferent from one color to another. Over time the combined color wouldchange noticeably if one of the LEDs fails or is degrading.

(2) Partially converting light in short wavelengths to light in thelonger wavelengths using phosphors. One of the most common ways is tocover a yellowish phosphor powder around a blue InGaN LED chip. Thephosphor powder is usually made of cerium doped yttrium aluminum garnet(YAG:Ce) crystals. Part of the blue light emitted by the InGaN LED chipis converted to yellow by the YAG:Ce. However, the “white” light soproduced contains mainly two colors: blue and yellow. Such a lightsource is usually used as indicator lamps.

(3) Using UV light produced by very short-wavelength LEDs to excitephosphors of different colors in order to produce light in three basiccolors. The drawback of this method is that the lifetime of the UV LEDsis relatively short. Furthermore, UV radiation from the LEDs can be ahealth hazard, as most of commonly used encapsulation materials todayare not effective in blocking UV radiation.

There have been numerous attempts in developing white LED light sourceswith higher efficiency and better chromaticity. Guo et al(“Photon-Recycling for High Brightness LEDs”, Compound Semiconductor6(4) May/June 2000) suggests the concept of photon recycling inproducing high brightness white LEDs. Photon recycling is a process bywhich short wavelength photons are absorbed by an emitter material,which re-emits photons of long-wavelengths. In principle, photonrecycling semiconductor (PRS) LEDs can efficiently produce white lightup to 330 lumen/watt. However, the drawback of PRS-LEDs is theirextremely low color-rendering index.

The dual-color PRS-LED, as disclosed in Guo et al., consists of aprimary light source and a secondary light source. The secondary lightsource has a secondary light-emitting layer. The primary light source isused to produce blue light. The produced blue light is directed to thesecondary emitting layer so that part of the blue light is absorbed inorder to produce yellow light in the re-emitting process. In principle,the dual-color photon production in PRS-LEDs is analogous to thephosphor coated LED. However, unlike the phosphor coated LED, thesecondary light source consists of a fluorescent semiconductor material,AlGaInP, directly bonded to the primary light source wafer. It istherefore possible to produce dual-color LED chips on a wafer. FIG. 1shows the structure of a PRS-LED, according to Guo et al. As shown inFIG. 1, the PRS-LED 1 consists of a transparent substrate 18 made ofsapphire. The primary light source and the secondary light source aredisposed on opposite sides of the sapphire substrate. The primary lightsource comprises a p-type GaN layer 12, an active layer 14 made fromInGaN and an n-type GaN layer 16. These layers are epitaxially grown onthe sapphire substrate 18. The secondary light source LED consists ofmainly a layer of AlGaInP 22. The AlGaInP layer is epitaxially grown ona GaAs substrate (not shown) and then bonded to the sapphire substrate18 using a bonding material 20. The GaAs substrate is subsequentlyremoved by chemically-assisted polishing and selective wet etching.After the primary light source layers are patterned, an n-type contact36 made of Al is deposited on a section of the n-type GaN layer 16, anda p-type contact 32 of Ni is deposited on a section of the p-type GaNlayer 12.

The primary light output is produced in the active region 14 by currentinjection, and the wavelength of the primary light is approximately 470nm. In operation, a portion of the photons emitted by the primary lightsource is absorbed by the AlGaInP layer 22 and then re-emitted (orrecycled) as photons of a longer wavelength. The composition of theAlGaInP layer 22 can be selected such that the re-emitted light is atthe wavelength of 570 nm (yellow). Because the colors of the lightproduced by the primary light source and the secondary light source arecomplementary, the combined light output appears white to the human eye.In such a PRS-LED structure, while the white light contains emissionpeaks of 470 nm (blue) and 570 nm (yellow), no red light (˜650 nm) isemitted.

The mixed light produced by the aforementioned methods may appear whiteto the human eye. However, the mixed light does not have the requiredchromaticity as required in a quality color display, such as an LCDdisplay.

Thus, it is advantageous and desirable to provide a method to produce asemiconductor light source containing wavelength components in RGB.

SUMMARY OF THE INVENTION

The present invention combines color components in a first PSR-LED withdifferent color components in a second PRS-LED to produce white-light ina white emitting device. The first PRS-LED has a primary light source toemit blue light and a secondary light source to emit red lightresponsive to the blue light; and the second PRS-LED has a primary lightsource to emit green light and a secondary light source for emitting redlight responsive to the green light. Each of the primary light sourcesis made from an InGaN layer disposed between a p-type GaN layer and ann-type GaN layer. The secondary light sources are made from AlGaInP orGa_(x)In_(1-x)P. The primary light source and the secondary light sourcecan be disposed on opposite sides of a sapphire substrate.Alternatively, the second light source is disposed on the n-type GaNlayer of the primary light source. The second light sources may comprisemicro-rods of AlGaInP of same or different compositions. AlGaN can alsobe used to replace p-GaN or n-GaN.

Thus, the first aspect of the present invention provides a method ofproducing a white-light emitting source, the white light comprising atleast a first color component with a first wavelength, a second colorcomponent with a second wavelength, and a third color component with athird wavelength, the first wavelength shorter than the secondwavelength, the second wavelength shorter than the third wavelength. Themethod comprises the steps of:

providing at least one first light emitting device, the first lightemitting device comprising a first light source for emitting the firstcolor component, and a second light source for emitting a part of thethird color component responsive to the first color component;

disposing at least one second light emitting device adjacent to thefirst light emitting device, the second light emitting device having afirst light source for emitting the second color component, and a secondlight source for emitting a further part of the third color componentresponsive to the second color component; and

combining the first color component and said part of the third colorcomponent emitted by the first light emitting device to the second colorcomponent and said further part of the third color component so as toproduce said white light.

According to the present invention, the first light source in the firstlight emitting device comprises:

a first active layer;

a hole source layer to provide holes to the first active layer; and

an electron source layer to provide electrons to the first active layerso that at least part of the electrons combine with at least part of theholes in the first active layer to produce light of the firstwavelength, and the first light source in the second light emittingdevice comprises:

a second active layer;

a hole source layer to provide holes to the second active layer; and

an electron source layer to provide electrons to the second active layerso that at least part of the electrons combine with at least part of theholes in the second active layer to produce light of the secondwavelength.

According to the present invention, the second light source in the firstlight emitting device and the second light source in the second lightemitting device are made substantially from AlGaInP, or Ga_(x)In_(1-x)P,where 0<x<1;

the first and second active layers are made substantially from InGaN;

the hole source layers are made substantially from a p-type GaN; and

the electron source layers are made substantially from an n-type GaN.

According to the present invention, the first color component is blue,the second color component is green and the third color component isred.

The second aspect of the present invention provides a light emittingdevice for emitting white-light of at least a first color component witha range of first wavelengths, a second color component with a range ofsecond wavelengths and a third color component with a range of thirdwavelengths, the first wavelengths shorter than the second wavelengths,the second wavelengths shorter than the third wavelengths. The lightemitting device comprises:

a mounting plate;

a first light emitting component disposed on the mounting plate, thefirst light emitting component comprising a first light source foremitting the first color component, and a second light source foremitting a part of the third color component responsive to the firstcolor component; and

a second light emitting component disposed on the mounting plateadjacent to the first light emitting component, the second lightemitting component having a first light source for emitting the secondcolor component, and a second light source for emitting a further partof the third color component responsive to the second color component.

According to the present invention, the first light source in the firstlight emitting component comprises:

a first active layer;

a hole source layer to provide holes to the first active layer; and

an electron source layer to provide electrons to the first active layerso that at least part of the electrons combine with at least part of theholes in the first active layer to produce light of the firstwavelength, and the first light source in the second light emittingcomponent comprises:

a second active layer;

a hole source layer to provide holes to the second active layer; and

an electron source layer to provide electrons to the second active layerso that at least part of the electrons combine with at least part of theholes in the second active layer to produce light of the secondwavelength.

According to one embodiment of the present invention, the first activelayer is disposed between the electron source layer and the hole sourcelayer in the first light emitting component, and the hole source layeris disposed on a first side of a first transparent substrate and thesecond light source in the first light emitting component is disposed ona second side of the first transparent substrate, and wherein the secondactive layer is disposed between the electron source layer and the holesource layer in the second light emitting component, and the hole sourcelayer is disposed on a first side of a second transparent substrate andthe second light source in the second light emitting component isdisposed on a second side of the second transparent substrate.

According to the present invention, one or more of the second lightsources in the first light emitting component and the second lightemitting component comprise a plurality of micro-rods of AlGaInP orGa_(x)In_(1-x)P, where 0<x<1.

According to the present invention, the second light source in the firstemitting component comprises a plurality of micro-rods of a firstAlGaInP layer and a second AlGaInP layer, the first AlGaInP layeremitting light in one third wavelength and the second AlGaInP layeremitting light in another third wavelength.

According to the present invention, the hole source, the first activelayer and the electron source layer in the first light emittingcomponent are sequentially deposited on the first transparent substratein an epitaxial growth process, and the second light source in the firstlight emitting component is bonded to the first transparent substratevia a bonding layer; and wherein the hole source, the second activelayer and the electron source layer in the second light emittingcomponent are sequentially deposited on the second transparent substratein an epitaxial growth process, and the second light source in thesecond light emitting component is bonded to the second transparentsubstrate via a bonding layer, and in which:

the transparent substrate comprises a sapphire substrate;

the first and second active layers are made substantially from InGaN;

the hole source layers are made substantially from p-GaN; the electronsource layer are made substantially from n-GaN, and the second lightsources in the first and second light emitting components are madesubstantially from AlGaInP or Ga_(x)In_(1-x)P, where 0<x<1.

According to another embodiment of the present invention, the firstactive layer is disposed between the electron source layer and the holesource layer in the first light emitting component, the hole sourcedisposed on a substrate, and the second light source in the first lightemitting component is disposed on the electron source layer in the firstlight emitting component, and wherein the second active layer isdisposed between the electron source layer and the hole source layer inthe second light emitting component, the hole source disposed on asecond substrate, and the second light source in the second lightemitting component is disposed on the electron source layer in thesecond light emitting component, in which:

the first and second active layers are made substantially from InGaN;

the hole source layers are made substantially from p-GaN;

the electron source layer are made substantially from n-GaN, and thesecond light sources in the first and second light emitting componentsare made substantially from AlGaInP or Ga_(x)In_(1-x)P, where 0<x<1.

According to the present invention, the first color component is a bluecolor component, the second color component is a green color component,and the third color component is a red color component.

The present invention will become apparent upon reading the descriptiontaken in conjunction with FIGS. 2 a-8.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic representation of a prior art white light LED.

FIG. 2 a to 2 h illustrate the method of producing component LEDs,according to present invention, in which:

FIG. 2 a shows various material layers disposed on a transparentsubstrate for producing the primary light source.

FIG. 2 b shows the layers being patterned.

FIG. 2 c shows the patterned layers having electrical contracts disposedthereon.

FIG. 2 d shows the reduction of the transparent substrate thickness.

FIG. 2 e shows an epitaxially grown AlGaInP layer on a semiconductorsubstrate.

FIG. 2 f shows the AlGaInP layer bonded to the different side of thetransparent substrate together with the semiconductor substrate.

FIG. 2 g shows the removal of the semiconductor substrate from thebonded structure, leaving the AlGaInP layer as a secondary light source.

FIG. 2 h shows the etching of the AlGaInP layer to produce a pluralityof micro-rods in the secondary light source.

FIG. 3 a to 3 e illustrate different shapes of the micro-rods in thesecondary light source; in which:

FIG. 3 a shows a two-level micro-structure;

FIG. 3 b shows a single-level micro-structure with micro-rods of uniformwidth.

FIG. 3 c shows a single-level micro-structure wherein the base of themicro-rods is wider than the top;

FIG. 3 d shows a single-level micro-structure wherein the base of themicro-rods is narrower than the base; and

FIG. 3 e shows a two-level micro-structure with two layers of differentmaterials.

FIG. 4 a is a schematic representation showing the white-light emittingdevice, according to one embodiment of the present invention.

FIG. 4 b is a schematic representation showing the white-light emittingdevice, according to another embodiment of the present invention.

FIG. 4 c is a schematic representation showing the white-light emittingdevice, according to another embodiment of the present invention.

FIG. 5 is a flowchart illustrating the method to fabricate thewhite-light emitting device as shown in FIG. 2 a-4 c.

FIG. 6 a to 6 g illustrate another method of producing component LEDs,according to present invention, in which:

FIG. 6 a shows various material layers disposed on a transparentsubstrate for producing the primary light source;

FIG. 6 b shows an epitaxially grown AlGaInP layer on a semiconductorsubstrate;

FIG. 6 c shows the AlGaInP layer bonded to the top layer of the primarylight source layers;

FIG. 6 d show the removal of the semiconductor substrate from the bondedstructure, leaving the AlGaInP layer as a secondary light source;

FIG. 6 e shows the patterned secondary and primary light source layers;

FIG. 6 f shows the patterned layers having electrical contracts disposedthereon; and

FIG. 6 g shows the etching of the AlGaInP layer.

FIG. 7 a is a schematic representation showing a white-light emittingdevice, according to a different embodiment of the present invention.

FIG. 7 b is a schematic representation showing a white-light emittingdevice, according to another different embodiment of the presentinvention.

FIG. 7 c is a schematic representation showing a white-light emittingdevice, according to yet another different embodiment of the presentinvention.

FIG. 8 is a flowchart illustrating the method to fabricate thewhite-light emitting device as shown in FIG. 6 a-7 c.

DETAILED DESCRIPTION OF THE INVENTION

In order to achieve three primary colors red, green and blue in thewhite-light source, the present invention uses at least two discretedual-color LEDs. A first dual-color LED emits red light and blue light,and a second dual-color LED emits red light and green light. As such,the combined light emission contains red light, green light and bluelight. The present invention provides two distinct embodiments of thewhite-emitting light devices produced by two different methods. FIGS. 2a to 2 h show a first method for producing dual-color LEDs, according tothe present invention.

FIG. 2 a shows various material layers disposed on a transparentsubstrate for producing a primary light source structure. As shown inFIG. 2 a, an n-type GaN layer 116 is epitaxially grown on a sapphiresubstrate 118. A layer 114 of blue-light emitting InGaN is epitaxiallygrown on the n-type GaN layer 116 and then a p-type GaN layer 112 isepitaxially grown on the InGaN layer 114. The combined layers are thenetched so as to produce a plurality of primary light source components,as shown in FIG. 2 b. As shown in FIG. 2 c, a plurality of electricalcontacts 136 are provided on the p-type layer 112, and a plurality ofelectrical contacts 132 are provided on the n-type layer 116. Thethickness of the sapphire substrate 118 can now be reduced to about 100μm, as shown in FIG. 2 d. Separately, an AlGaInP layer 122 isepitaxially grown on a semiconductor substrate, such as a GaAs wafersubstrate 128, as shown in FIG. 2 e. The AlGaInP layer 122 is bonded tothe different side of the sapphire substrate 118 using a spin-on-glass(SOG) method, for example. The bonding layer between the AlGaInP layer122 and the sapphire substrate 118 is denoted by reference numeral 120,as shown in FIG. 2 f. In this illustrative example, the primary lightsource layers 112, 114 and 116 are chosen to emit blue light.Accordingly, the AlGaInP layer 122 is selected to produce red light as asecondary light source by absorbing the blue light emitted from theprimary light source layers through the sapphire layer 118.

Now the semiconductor substrate 128 is removed by a 1NH₄OH:1H₂O₂:10H₂Osolution in a wet etching process, as shown in FIG. 2 g, in order toexpose the AlGaInP layer 122. The processed layer structure can now becut into small dies 100. While the height of the dies 100 is determinedby the thickness of various layers, the area of the dies can be 300μm×365 μm, for example. It should be noted that the thickness of theAlGaInP layer 122 can significantly affect the color and the lightoutput of the dual-color LED die 100. If the AlGaInP layer 122 is toothick, the blue light may be excessively reduced by the absorption inthe AlGaInP layer 122. If the layer 122 is too thin, the portion of theshort wavelength photons being absorbed may be too small to produceenough red light from the AlGaInP layer in the re-emitting process.However, it is possible to adjust the relative amount of blue light andred light by selectively removing part of the AlGaInP layer 122. Asshown in FIG. 2 h, the AlGaInP layer 122 is patterned by variousdry-etching techniques into a patterned AlGaInP layer 122 a. The furtherprocessed layer structures can now be cut into a plurality of small dies100 a. It should be noted that each of the small dies 100 a or 100 canbe used as a blue-red emitting component in the white-light emittingdevice, according to the present invention. In order to produce thegreen-red emitting components, processes similar to those shown in FIGS.2 a to 2 h are used except that the InGaN layer is now a green-emittinglayer 114′, and the AlGaInP layer is now a layer 122′ for re-emittingred light after the absorption of green light.

There is more than one way to pattern the AlGaInP layer 122 in order toimprove the light emitting efficiency of the dual-color LEDs. Forexample, the AlGaInP layer 122 can be etched to form an array oftwo-level micro-rods as shown in FIG. 3 a, or single-level micro-rods asshown in FIG. 3 b. The single-level micro-rods can have differentshapes. For example, the base of the single-level micro-rods can bewider than the top of the micro-rods, as shown in FIG. 3 c.Alternatively, the top of the single-level micro-rods can be wider thanthe base of the micro-rods, as shown in FIG. 3 d. The structured AlGaInPlayer is denoted by reference numeral 122 a. It should be noted that thetwo-level micro-rods can be made substantially of the same AlGaInPcomposition, as shown in FIG. 3 a. However, they can also be two layers123 a, 123 b made from AlGaInP of different compositions, as shown 3 e.For example, one layer emits light at 630 nm and the other at 670 nm.These different compositions improve the color rendering ability of thewhite light-emitting device. It is understood that the shapes and thesizes of the micro-rods shown in FIGS. 3 a-3 d are for illustrativepurposes only. The micro-rods need not be regular or retain a certaingeometrical shape. The main purpose of etching the AlGaInP layer 122 isto adjust the relative amount of light produced by the primary lightsource to that by the secondary light source through the top of thedual-color LED.

The white-light emitting device, according to one embodiment of thepresent invention, is shown in FIG. 4 a. As shown, the white-lightemitting device 300 comprises at least one blue-red emitting LED 100 aand one green-red emitting LED 100 a′. Both LEDs 100 a and 100 a′ aremounted on various electrically conductive sections 172, 174 and 176 ona baseboard 180. Electrical contacts 152, 156 and wire bonds 162, 166are further provided on the baseboard so as to provide an electricalcurrent through the LEDs connected in series. Alternatively, only one ofthe dual-color LEDs has a patterned AlGaInP layer 122 a, as shown inFIG. 4 b. It is also possible that the AlGaInP layer 122 on each of thedual-color LEDs 100, 100′ be an un-etched layer, as shown in FIG. 4 c.

FIG. 5 is a flowchart illustrating the method to produce the white-lightemitting device 300, according to the present invention. As shown in theflowchart 500, a step 510 is used to produce a blue LED layer structureon a sapphire substrate (see FIG. 2 a) and a green LED layer structureon a different sapphire substrate. The step 520 is used to reduce thethickness of the sapphire substrate (see FIG. 2 d). The step 530 is usedto produce a red emitting thin film layer on a semiconductor substrate(see FIG. 2 e). The red emitting thin film layer is bonded to adifferent side of the sapphire substrate at step 540 (see FIG. 2 f) andthe semiconductor substrate is removed from the bonded structure at step550 (see FIG. 2 g). It may be desirable to pattern the red emitting thinfilm layer at an optional step 560 (see FIG. 2 h). The combined blue-redemitting layer structure and the combined green-red emitting layerstructure are cut into smaller dies at step 570.

At least one blue-red LED component and one green-red LED component aremounted on a baseboard at step 580 and electrical contacts are providedto the dies at step 590 (see FIG. 4 a-4 c).

FIGS. 6 a to 6 g show a second method for producing dual-color LEDs,according to the present invention.

FIG. 6 a shows various material layers disposed on a transparentsubstrate for producing a primary light source structure. As shown inFIG. 6 a, an n-type GaN layer 116 is epitaxially grown on a sapphiresubstrate 118. A layer 114 of blue-light emitting InGaN is epitaxiallygrown on the n-type GaN layer 116 and then a p-type GaN layer 112 isepitaxially grown on the InGaN layer 114. Separately, an AlGaInP layer122 is epitaxially grown on a semiconductor substrate, such as a GaAswafer substrate 128, as shown in FIG. 6 b. The AlGaInP layer 122 isbonded to the top of the primary light source layers—the p-type GaNlayer 112, as shown in FIG. 6 c. The bonding layer between the AlGaInPlayer 122 and p-type GaN layer 112 is denoted by reference numeral 121,as shown in FIG. 6 c. In this illustrative example, the primary lightsource layers 112, 114 and 116 are chosen to emit blue light.Accordingly, the AlGaInP layer 122 is selected to produce red light as asecondary light source by absorbing the blue light emitted from theprimary light source layers through the sapphire layer 118.

Now the semiconductor substrate 128 is removed by a 1NH₄OH:1H₂O₂:10H₂Osolution in a wet etching process, as shown in FIG. 6 d, in order toexpose the AlGaInP layer 122. The bonded structure is further patternedso as to produce a plurality of dual-color LED components, as shown inFIG. 6 e and electrical contacts 132, 136 are provided, respectively, tothe p-type layer 112 and the n-type layer 116 as shown in FIG. 6 f. Theprocessed layer structure can now be cut into small dies 105. It may bedesirable to remove part of the AlGaInP layer 122 in order to adjust therelative amount of light emitted by the primary light source to that bythe secondary light source through the AlGaInP layer 122. As shown inFIG. 6 g, the AlGaInP layer 122 is patterned by various dry-etchingtechniques into a patterned AlGaInP layer 122 a. The further processedlayer structures can now be cut into a plurality of small dies 105 a.Each of the small dies 105 a or 105 can be used as a blue-red emittingcomponent in the white-light emitting device, according to the presentinvention. In order to produce the green-red emitting components,processes similar to those shown in FIGS. 6 a to 6 g are used exceptthat the InGaN layer is now a green-emitting layer 114′, and the AlGaInPlayer is now a layer 122′ for re-emitting red light after the absorptionof green light. The white-light emitting device, according to thissecond embodiment of the present invention, is shown in FIG. 7 a. Asshown, the white-light emitting device 400 comprises at least oneblue-red emitting LED 105 a and one green-red emitting LED 105 a′. BothLEDs 105 a and 105 a′ are on a baseboard 190. Electrical contacts 154,158 and wire bonds 164, 167 and 168 are further provided on thebaseboard 190 and various contacts 132, 136 so as to provide anelectrical current through the LEDs connected in series. Alternatively,only one of the dual-color LEDs has a patterned AlGaInP layer 122 a, asshown in FIG. 7 b. It is also possible that the AlGaInP layer 122 oneach of the dual-color LEDs 105, 105′ be an un-etched layer, as shown inFIG. 7 c.

FIG. 8 is a flowchart illustrating the method to produce the white-lightemitting device 400, according to the present invention. As shown in theflowchart 600, a step 610 is used to produce a blue LED layer structureon a sapphire substrate (see FIG. 6 a) and a green LED layer structureon a different sapphire substrate. The step 620 is used to produce a redemitting thin film layer on a semiconductor substrate (see FIG. 6 b).The red emitting thin film layer is bonded to the top of the primarylight source layer at step 630 (see FIG. 6 c) and the semiconductorsubstrate is removed from the bonded structure at step 640 (see FIG. 6d). The combined secondary and primary light emitting layers arepatterned and then provided electrical contacts at step 650 (see FIGS. 6e and 6 f). It may be desirable to pattern the red emitting thin filmlayer at an optional step 660 (see FIG. 6 g). The combined blue-redemitting layer structure and the combined green-red emitting layerstructure are cut into smaller dies at step 670. At least one blue-redLED component and one green-red LED component are mounted on a baseboardat step 680 and electrical contacts are provided to the dies at step 690(see FIG. 7 a-7 c).

It should be noted that each of the dual-color LEDs 100, 105, 100′, 105′has a primary light source and a secondary light source. In thedual-color LEDs 100, 100′, the primary light source and the secondarylight source are disposed on different side of the transparent substrate118. In order to reduce the loss of the light emitted by the primarylight source by absorption in the substrate 118, the thickness of thesubstrate 118 is reduced to approximately 100 μm. In the dual-color LEDs105, 105′, the primary light source and the secondary light source aredisposed on the same side of the transparent substrate 118, with thesecondary light source bonded to the top layer of the primary lightsource. It would not be necessary to reduce the thickness of thetransparent substrate 118.

It should be appreciated by person skilled in the art that the red lightemitting layer 122 (FIGS. 2 e-4 c and 6 b-6 g, for example) can be alsomade of Ga_(x)In_(1-x)P, where 0<x<1. Furthermore, the p-GaN layer 112is a hole source for providing holes to the active layer 114, and then-GaN layer 116 is an electron source for providing electrons to theactive layer 114 so that part of the holes combine with part of theelectrons in the active layer 114 to produce blue or green light. AlGaNcan also be used in some cases to replace p-GaN in the hole source layer112 and to replace n-GaN in the electron source layer 116.

In sum, the white-light emitting device of the present inventioncomprises at least one blue-red LED and one green-red LED. These LEDscan be electrically connected in series. In one embodiment of thepresent invention, the dual-color LED comprises a primary light sourceand a secondary light source disposed on different sides of atransparent substrate. In the other embodiment of the present invention,the dual-color LED comprises a primary light source disposed on asubstrate and a secondary light source bonded to the primary lightsource. It should be noted that it is possible to have more than oneblue-red LED disposed in one white-light emitting device, according tothe present invention. Likewise, it is also possible to have more thanone green-red LED disposed in one white-light emitting device. Thenumber of the dual-color LEDs in one white-light emitting devicepartially depends upon the desirable white-light intensity and partiallyupon the relative amount in the light components in RGB.

Although the invention has been described with respect to one or moreembodiments thereof, it will be understood by those skilled in the artthat the foregoing and various other changes, omissions and deviationsin the form and detail thereof may be made without departing from thescope of this invention.

1-20. (canceled)
 21. A method of producing a white-light emittingsource, the white light comprising at least a first color component witha first wavelength, a second color component with a second wavelength,and a third color component, said method comprising the steps of:disposing a first light emitting device on a first side of a firsttransparent substrate, the first light emitting device comprising afirst light source for emitting the first color component; disposing asecond light emitting device on a first side of a second transparentsubstrate, the second light emitting device comprising a second lightsource for emitting the second color component; disposing a third lightemitting device on at least one semiconductor substrate; separatelybonding a second side of the first transparent substrate to the thirdlight-emitting device for forming a first light emitting structure andbonding a second side of the second transparent substrate to the thirdlight-emitting device for forming a second light emitting structure;removing said at least one semiconductor substrate from the first lightemitting structure for providing a reduced first light emittingstructure; removing said at least one semiconductor substrate from thesecond light emitting structure for providing a reduced second lightemitting structure; dividing the reduced first light emitting structureinto a plurality of first combined light-emitting dies; dividing thereduced second light emitting structure into a plurality of secondcombined light-emitting dies; mounting at least one first combinedlight-emitting die and at least one second combined light-emitting dieon a baseboard; and providing electrical contacts to said at least onefirst combined light-emitting die and said at least one second combinedlight-emitting die.
 22. The method of claim 21, further comprising thestep of: reducing the thickness of the first transparent substrate andthe thickness of the second transparent substrate prior to said bonding.23. The method of claim 21, further comprising the step of: producingmicrostructure on the third light emitting device after removing said atleast one semiconductor substrate from the first light emittingstructure for providing a reduced first light emitting structure andremoving said at least one semiconductor substrate from the second lightemitting structure for providing a reduced second light emittingstructure.
 24. The method of claim 21, wherein the first light-emittingdevice comprises: a first active layer; a hole source layer to provideholes to the first active layer; and an electron source layer to provideelectrons to the first active layer so that at least part of theelectrons combine with at least part of the holes in the first activelayer to produce light of the first wavelength, and wherein the secondlight-emitting device comprises: a second active layer; a hole sourcelayer to provide holes to the second active layer; and an electronsource layer to provide electrons to the second active layer so that atleast part of the electrons combine with at least part of the holes inthe second active layer to produce light of the second wavelength. 25.The method of claim 24, wherein the first and second active layers aremade substantially of InGaN; the hole source layers are madesubstantially of a p-type GaN; and the electron source layers are madesubstantially of an n-type GaN.
 26. The method of claim 21, wherein thethird light-emitting device is made substantially from AlGaInP.
 27. Themethod of claim 21, wherein the third light-emitting device is madesubstantially of Ga_(x)In_(1-x)P, where 0<x<1.
 28. The method of claim21, wherein the third light-emitting device is made substantially ofGa_(x)In_(1-x)P, where 0.3<x<0.7.
 29. The method of claim 21, whereinthe third light-emitting device comprises a plurality of micro-rods madesubstantially of AlGaInP or Ga_(x)In_(1-x)P, where 0.3<x<0.7.
 30. Themethod of claim 21, wherein the third light-emitting device comprises aplurality of micro-rods of a first AlGaInP layer and a second AlGaInPlayer, the first AlGaInP layer emitting light in one third wavelengthand the second AlGaInP layer emitting light in another third wavelength.31. A method of producing a white-light emitting source, the white lightcomprising at least a first color component with a first wavelength, asecond color component with a second wavelength, and a third colorcomponent, said method comprising the steps of: disposing a first lightemitting device on a first side of a first transparent substrate, thefirst light emitting device comprising a first light source for emittingthe first color component; disposing a second light emitting device on afirst side of a second transparent substrate, the second light emittingdevice comprising a second light source for emitting the second colorcomponent; disposing a third light emitting device on at least onesemiconductor substrate; separately bonding a second side of the firsttransparent substrate to the third light-emitting device for forming afirst light emitting structure and bonding a second side of the secondtransparent substrate to the third light-emitting device for forming asecond light emitting structure; removing said at least onesemiconductor substrate from the first light emitting structure forproviding a reduced first light emitting structure; removing said atleast one semiconductor substrate from the second light emittingstructure for providing a reduced second light emitting structure;patterning the reduced first and second light-emitting structures intopatterned first and second light-emitting structures; providingelectrical contacts in the patterned first and second light emittingstructures; dividing the patterned first light emitting structure into aplurality of first combined light-emitting dies; dividing the patternedsecond light emitting structure into a plurality of second combinedlight-emitting dies; mounting at least one first combined light-emittingdie and at least one second combined light-emitting die on a baseboard;and providing electrical contacts to said at least one first combinedlight-emitting die and said at least one second combined light-emittingdie.
 32. The method of claim 31, further comprising the step of:producing microstructure on the third light emitting device afterremoving said at least one semiconductor substrate from the first lightemitting structure for providing a reduced first light emittingstructure and removing said at least one semiconductor substrate fromthe second light emitting structure for providing a reduced second lightemitting structure.
 33. The method of claim 31, wherein the firstlight-emitting device comprises: a first active layer; a hole sourcelayer to provide holes to the first active layer; and an electron sourcelayer to provide electrons to the first active layer so that at leastpart of the electrons combine with at least part of the holes in thefirst active layer to produce light of the first wavelength, and whereinthe second light-emitting device comprises: a second active layer; ahole source layer to provide holes to the second active layer; and anelectron source layer to provide electrons to the second active layer sothat at least part of the electrons combine with at least part of theholes in the second active layer to produce light of the secondwavelength.
 34. The method of claim 33, wherein the first and secondactive layers are made substantially of InGaN; the hole source layersare made substantially of a p-type GaN; and the electron source layersare made substantially of an n-type GaN.
 35. The method of claim 31,wherein the third light-emitting device is made substantially fromAlGaInP.
 36. The method of claim 31, wherein the third light-emittingdevice is made substantially of Ga_(x)In_(1-x)P, where 0<x<1.
 37. Themethod of claim 31, wherein the third light-emitting device is madesubstantially of Ga_(x)In_(1-x)P, where 0.3<x<0.7.
 38. The method ofclaim 31, wherein the third light-emitting device comprise a pluralityof micro-rods made substantially of AlGaInP or Ga_(x)In_(1-x)P, where0.3<x<0.7.
 39. The method of claim 31, wherein the third light-emittingdevice comprises a plurality of micro-rods of a first AlGaInP layer anda second AlGaInP layer, the first AlGaInP layer emitting light in onethird wavelength and the second AlGaInP layer emitting light in anotherthird wavelength.
 40. A light emitting device for emitting white-lightof at least a first color component with a range of first wavelengths, asecond color component with a range of second wavelengths and a thirdcolor component with a range of third wavelengths, the first wavelengthsshorter than the second wavelengths, the second wavelengths shorter thanthe third wavelengths, said light emitting device comprising: a mountingplate; a first light emitting component disposed on the mounting plate,the first light emitting component comprising a first light source foremitting the first color component, and a second light source foremitting a part of the third color component responsive to the firstcolor component; and a second light emitting component disposed on themounting plate adjacent to the first light emitting component, thesecond light emitting component having a first light source for emittingthe second color component, and a second light source for emitting afurther part of the third color component responsive to the second colorcomponent, wherein the first active layer is disposed between theelectron source layer and the hole source layer in the first lightemitting component, and the hole source layer is disposed on a firstside of a first transparent substrate and the second light source in thefirst light emitting component is disposed on a second side of the firsttransparent substrate, and wherein the second active layer is disposedbetween the electron source layer and the hole source layer in thesecond light emitting component, and the hole source layer is disposedon a first side of a second transparent substrate and the second lightsource in the second light emitting component is disposed on a secondside of the second transparent substrate, and wherein the second lightsource in the first light emitting component is substantially made ofAlGaInP or Ga_(x)In_(1-x)P, where 0.3<x<0.7.
 41. The device of claim 40,wherein the second light source in the second light emitting componentis substantially made of AlGaInP or Ga_(x)In_(1-x)P, where 0.3<x<0.7.